When deprived of much-needed naps, toddlers become stressed, joyless, and easily rattled. So basically, just like sleep-deprived adults. And as a bonus, scientists think lack of naps could mess toddlers up for life.

A EurekAlert press release reports that researchers made sure their sample of two- and three-year-olds got regular nighttime sleep and naps for five days before the experiment. Then they deprived the kids of their daily nap, which must have been momentarily exciting because everyone knows naptime sucks when you're a toddler. But the reprieve came with a price — sadistic researchers gave them two puzzles to solve, one of which was actually unsolvable. They then watched the kids' little faces contort in agony as they struggled with the impossible task. And later, when the kids were well-rested, they tested them again as a control.

The result: kids who didn't nap showed "more anxiety, less joy and interest and a poorer understanding of how to solve problems" than when they were fully rested. They were less happy when they solved a puzzle correctly, and more upset when confronted with an insoluble one. They were also less apt to display confusion, which study author Monique LeBourgeois says is actually a positive emotion that prompts toddlers to seek help in solving problems. Presumably, the underslept toddlers just stared numbly at the puzzle pieces, viewing them as a metaphor for the misery and meaninglessness of their lives. And LeBourgeois says things can only get worse:

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Many young children today are not getting enough sleep, and for toddlers, daytime naps are one way of making sure their 'sleep tanks' are set to full each day. This study shows insufficient sleep in the form of missing a nap taxes the way toddlers express different feelings, and, over time, may shape their developing emotional brains and put them at risk for lifelong, mood-related problems.

The study didn't appear to include a longitudinal component, so the authors don't really have evidence that missing a nap from time to time will make two-year-olds grow up into serial killers. However, given the fact that sleep deprivation appears to affect toddlers pretty much exactly the way it affects the rest of us — making them cranky, ill-adjusted, and incapable of true happiness — it's a safe bet that you should make sure your kids get enough sleep. And don't give them unsolvable puzzles — that's just mean.